Medical electrodes are well known in the art and vary considerably in their structure and configuration. They generally have a substrate designed to be applied and held to the skin of a patient, an electrical connector, and a conductive lead wire removably and electrically attached to the electrical connector on one end and to a monitoring device on its opposite end. The field is relatively crowded.
Designs are usually controlled by, first, a requirement for a secure fastening of the electrical connector to the skin because the electrode may be part of a life support system. A second requirement of an electrode design is controlled by economics. There is a continuing need for high quality but inexpensive medical electrodes. For purposes of convenience and safety (e.g., to maintain sterility in a medical environment), the electrode should be sufficiently inexpensive to manufacture that it is practical to dispose of and to replace the electrode after only one use (hence, the electrode must be "disposable").
The various medical electrode designs can generally be placed into two categories. In one category are snap-type electrodes in which one end of the electrical connector terminates in a projecting snap or stud. The lead wire is provided with a mating eyelet or socket which receives and secures, by snapping over, the snap. An advantage of such an electrode is that it permits rotation between the electrode and the lead wire. Rotation assures patient comfort, prevents the electrode from disengaging when the patient moves, and allows connection between the lead wire and electrical connector without regard to orientation.
It is common to form the projecting snap from a non-conducting substrate and then to coat that substrate with a very thin coating of a conductive material. The thin coating of conducting material is easily abraded away, however, when the outer wall of the snap frictionally contacts and slides against the eyelet, as happens when the snap electrode rotates with respect to its lead wire. The resulting abrasion of the mating surfaces of the snap and eyelet can eventually degrade the electrical conductivity between the electrode and the lead wire.
To minimize the rotation between the electrode and lead, and the consequent degradation, some electrodes prevent relative rotation. Such electrodes restrict the versatility and ease of manipulation for the electrode, as well as the equipment to which the electrode is connected.
Another problem with the snap-type electrodes is that they have a relatively high profile (height). The snap must project from the electrode a significant distance to allow connection of the lead wire eyelet. A high profile is disadvantageous because it makes the electrode more noticeable and increases the risk of damage by hitting other objects during use and storage. The electrical contacts between the snap and the lead wire eyelet and between the electrode and the patient are essential; those contacts must be protected from disengagement. Consequently, a low profile electrode is preferable.
The second type of electrode has no projecting snap or stud. It is usually thin, flat, flexible, disposable, snapless, and, therefore, substantially less expensive to manufacture or use. The lead wire interconnects the second type of electrode by engaging the electrode itself, usually at a lateral extension or tab at one side or at the center of the electrode. Thus, this second type of electrode is referred to as a "tab" electrode.
One problem with the tab electrode is that it typically does not permit rotation between the electrode and the lead wire. A particular orientation of the lead wire with respect to the tab of the electrode is required. Another problem is that tab electrodes generally are connected to their lead wires by spring or alligator clips affixed to the tab. Such clips typically give the clip-electrode combination a high profile. Moreover, the clips occasionally slip off the tab, rip through the tab, or tear the tab away from the remainder of the electrode and, therefore, are not entirely satisfactory under certain circumstances.
Regardless of the design, both snap-type and tab-type conventional medical electrodes are relatively complex in their structure. Many of these electrodes have hard, bulky components which make them uncomfortable to the patient. Most suffer from motion artifacts.
Motion artifacts can be defined as motion-induced fluctuation of skin potential. Such artifacts create electrical interference which is often superimposed on the bipotential skin signal measured by the electrode, thereby reducing the electrode's usefulness as a diagnostic and clinical tool. Motion artifacts have long been a problem in measuring biopotentials, particularly in long-term electrocardiogram (ECG or EKG) monitoring of coronary care patients and in exercise (stress) ECG's.
Artifacts are generally caused by movement of the patient (who may be on a moving treadmill, for example, to induce increased heart and respiratory rates) relative to the electrode applied to the patient's skin. That movement disturbs the skin potential and creates extraneous output on the monitor which either masks the desired bipotential signal or shifts the base line.
As the above discussion makes evident, the problem of providing a highly reliable, disposable, low profile electrode has presented a major challenge to designers in the health care field. The development of an economical, tabless (so orientation is eliminated) medical electrode would represent a major technological advance in the field. The advantages of such a device would satisfy a long-felt need within the medical profession.
Therefore, to overcome the shortcomings of the existing medical electrodes and to satisfy the need of the medical profession, a new, snapless, tabless, disposable medical electrode is provided. A primary object of the present invention is to provide an improved medical electrode which can be manufactured at low cost yet meets the structural requirements of the market. A related object is to provide an electrode which is economical and simple in design, yet durable and highly effective to use.
Patient comfort is an overriding concern with any electrode design. Accordingly, it is an object of the present invention to assure patient comfort. At the same time, rotational movement between the lead wire and electrode may be necessary to provide a good electrical connection. Such connection must be assured even when the patient moves. Accordingly, it is another object of the present invention to assure significant rotational movement between the lead wire and the electrode. It is still another object of the present invention to reduce motion artifacts.
An additional object is to assure that the electrode has a very low profile. Yet another object of this invention is to allow for quick and easy attachment and detachment, both to and from the patient and between the electrode and its lead wire, without concern for a specific orientation. Both types of attachment and detachment should be sufficiently simple that they can be done in the dark.